1. Field of the Invention
This invention relates generally to computer data storage drives and more specifically to a slider suspension and a corresponding retention and retraction system configured to eliminate slider/disk stiction in densely packed data storage drives.
2. Description of the Related Art
Suspension systems are employed in magnetic disk drives. A suspension system includes a head/gimbal assembly (HGA) which is either connected to an outer end ("suspended" end) of a load beam or is integral with the load beam itself and forms part of the outer end of the load beam. The HGA includes a flexure having a window bounded in part by a pair of flexure legs and an outer terminal end portion. Extending inward from the outer terminal end portion is a flexure tongue which is cantilevered into the window. A slider, carrying a magnetic head, is mounted at its bottom to a top of the tongue. A top surface of the slider and a pole tip portion of the magnetic head form an air bearing surface (ABS). An inner end of the load beam is connected to an actuator arm for moving the ABS across a surface of a magnetic disk while a spring force of the load beam preloads the ABS of the slider toward the magnetic disk.
When the disk is rotated, the ABS of the slider is supported ("flies") a slight distance from the surface of the disk, in the order of 0.075 um, on a cushion of air (air bearing) which counterbalances the preloading, the air bearing being created by the rotating disk. The actuator then moves the load beam to position one or more sliders at desired concentric tracks on the disks for reading and writing by the magnetic heads. The slider is gimbal supported by the HGA as it flies with respect to the disk.
A high capacity magnetic disk drive employs a plurality of double sided magnetic disks in a disk stack assembly and a plurality of suspension systems in a head stack assembly. The suspension systems, which are supported by an actuator assembly, are interleaved between the disks so that each side of each disk can be read and written by a respective magnetic head. Sliders of top and bottom suspensions in the stack face top and bottom surfaces of top and bottom disks and sliders of each pair of suspension systems between the top and bottom suspensions face opposing surfaces of a respective pair of disks. The surface facing the disk is the ABS surface. The top and bottom suspension of one actuator arm are referred to as a suspension pair.
It has long been recognized that it is necessary to retract or move away a slider from a disk if there is insufficient angular velocity of the disk to maintain a flying relationship with the slider. If the slider is not retracted then there will be increased stationary frictional forces that must be overcome to move the slider relative to the disk. These forces are known in the art as "stictional" forces. Stiction must be eliminated in a high capacity magnetic disk drive for each slider that is part of a slider suspension pair. The difficulty of the task is exacerbated by the fact that one slider of the pair faces one surface of a first disk and the other slider of the pair faces in an opposite direction toward the surface of a second disk. U.S. Pat. No. 5,231,549 to Morehouse et al. describes one technique for retracting a slider from a disk in a disk drive having a plurality of disks arranged in a disk stack assembly. The '549 patent discloses an actuator arm that has a cam follower which moves along a cam surface placed along the side of the disk. The cam surface serves as a ramp for lifting a slider that is attached to a suspension that is itself attached to the arm. Similar unloading ramps are described in other patents issued to Morehouse et al., including U.S. Pat. Nos. 5,289,325, 5,237,472, and 4,933,785. The ramp or cam surface described in each of these patents fits in the space between disks and engages the cam follower on the suspension. The inventors of this invention have recognized that such an arrangement is problematic because disk spacing is something that is constantly being reduced in the development of storage systems as the number of disks required to be stacked in a high capacity disk drive continues to be increased. Consequently, the amount of space available for such a ramp is also decreased. As disk spacing decreases, such a ramp configuration will likely be rendered infeasible because there will not be sufficient space to fit the ramp. It is also recognized by the inventors of the present invention that the complication of having to move one slider attached to one suspension in one direction and the other suspension of a suspension pair in another direction will also make such a ramp configuration unworkable as space is reduced because a separate space-consuming ramp is required for each slider.
What is needed is the capability to move a slider away from a disk in a high capacity disk drive system without requiring any more space between the disks than is required to accommodate an actuator arm having a slider suspension pair.